The present invention relates to a lower structure of an automotive vehicle which comprises a suspension cross member provided behind a power unit and extending in a vehicle width direction and a plate-shaped vehicle-body-side support portion supporting the suspension cross member.
Many structures which can absorb the vehicle-collision energy at a vehicle front portion in order to restrain the collision load from having bad influence on passengers in the vehicle room in a vehicle frontal collision or the like have been proposed.
For example, Japanese Patent Laid-Open Publication No. 2004-130827 discloses a structure in which a through hole is provided, in the vicinity of a bolt hole, at a lower wall portion of a suspension cross member attachment portion of a front side member (front frame). In this structure, when a load of specified value or more acts on a bolt in the vehicle frontal collision, this bolt moves, expanding the bolt hole, and reaches the through hole. Thereby, the suspension cross member can be allowed to move rearwardly greatly relative to the front side member. In this case, since a smooth retreat of a power unit is not hindered by the suspension cross member, the absorption of the collision energy can be achieved securely by the retreat of the power unit.
US Patent Application Publication No. 2005/0077754 discloses a structure in which a pipe-nut upper end portion as a connecting member to connect a vehicle-body-side front frame to a chassis frame (suspension cross member) is supported at a vehicle-body-side plate member, and when a load of specified value or more acts in the vehicle frontal collision, the plate member gets broken, so that its connection to the pipe nut is released. Thus, the chassis frame can be detached from the vehicle body in this structure, so that it can be prevented that the retreat of the power unit is hindered by the chassis frame.
Japanese Patent Laid-Open Publication No. 6-298121 discloses a structure in which in a vehicle equipped with front wheels arranged in front of an engine as a power unit, there is provided a bead to cause deformation of a suspension cross member by the collision energy in the vehicle collision. In this structure, the front wheels move back according to a rearward slant of a suspension arm by the deformation of the suspension cross member in the vehicle frontal collision. Accordingly, a plastically-deformable portion of a side frame increases, so that an increase of the collision-energy absorption can be achieved.
Japanese Patent Laid-Open Publication No. 2006-240325 discloses a structure in which a collar, a rear portion of which is not connected to the vehicle-body-side suspension cross member, is provided at a connection portion of the suspension cross member to the vehicle-body-side side member in order to prevent that the retreat of the power unit is hindered by the power unit in the vehicle frontal collision. In this structure, as the suspension cross member moves rearwardly in the vehicle collision, the connection portion rotates rearwardly easily. Thereby, the connection portion, that is, the suspension cross member can be detached off the vehicle body easily.
Japanese Patent Laid-Open Publication No. 2008-56191 discloses a structure in which a bending promotion portion is formed at a middle portion of a side frame constituting a sub frame, and the middle portion of the side frame and the sub frame are connected by a middle support member and a connecting member. In this structure, as the power unit retreats relatively in the vehicle frontal collision, the side frame bends due to the function of the bending promotion portion, and the connection between the middle support member and the connecting member is released. Consequently, the suspension cross member can be detached from the side frame.
However, according to the structure disclosed in the above-described first patent document, since the through hole is formed near a connection portion, the rigidity of part of the vehicle near the connection portion decreases during the normal vehicle traveling. Thus, there is a concern that the support rigidity of the suspension cross member would be improperly low. Further, since the bolt is fixed firmly to the vehicle body in the normal state, the bolt may not be moved right away when the vehicle collision occurs. Accordingly, there is a problem in that the suspension cross member could not be moved smoothly.
According to the structure disclosed in the above-described second patent document, further, the plate member may not be broken right away after the occurrence of the vehicle collision for the reason described above in the structure disclosed in the first patent document. Thus, there is also a problem in that the suspension cross member could not be detached smoothly.
According to the structure disclosed in the above-described third patent document, meanwhile, there is no concept that it can be prevented by releasing the connection between the suspension cross member and the vehicle body that the smooth retreat of the power unit is hindered. Further, this structure may not sufficiently increase the collision-energy absorption which is conducted at the vehicle front portion. Accordingly, it would be impossible to properly restrain the collision load from having bad influence on passengers.
According to the structure disclosed in the above-described fourth patent document, there is formed a gap between a sub side member and the suspension cross member so that the connection portion between the vehicle body (sub side member) and the suspension cross member can rotate rearwardly easily. However, this gap may cause a decrease of the rigidity of the part of the vehicle near the connection portion during the normal vehicle traveling, so that there is a concern that the support rigidity of the suspension cross member would be improperly low.
According to the structure disclosed in the above-described fifth patent document, an opening is formed in front of a through hole into which a bolt fastening the side frame and the suspension cross member is inserted (see FIG. 3 in this patent document). In this case, the rigidity of a vehicle part near this bolt connection portion may be improperly low, so that there is a concern that the support rigidity of the suspension cross member would be decreased. Further, since the connection between the middle support member and the connection member is released by the moving bolt itself, this releasing may not be conducted right away after the occurrence of the vehicle collision for the reason described above in the structures disclosed in the first and second patent documents. Thus, there is also a problem in that the suspension cross member could not be detached smoothly.